Enhanced phoretic self-propulsion of active colloids through surface charge asymmetry

Abstract: Charged colloidal particles propel themselves through asymmetric fluxes of chemically generated ions on their surface. We show that asymmetry in the surface charge distribution introduces a new mode of self-phoretic motion for chemically active particles that produce ionic species. Particles of sizes smaller than or comparable to the Debye length achieve directed self-propulsion through surface charge asymmetry even when ionic flux is uniform over the particle surface. Janus nanoparticles endowed with both surface charge and ionic flux asymmetries results in enhanced propulsion speeds of the order of $\mu$m/s or higher. Our work provides a theoretical framework to quantitatively determine the velocity of asymmetrically charged nanoparticles undergoing ionic self-diffusiophoresis, and suggests an avenue for specifying surface properties that optimize and regulate self-propulsion in ionic media.